1. Field of the Invention
The invention relates to a recording head and a recording apparatus, which applies thermal energy to a liquid and discharges the liquid through a nozzle, and an inspection apparatus of the recording head and a method thereof.
2. Description of the Related Art
An inkjet recording apparatus, e.g., an inkjet printer, prints a variety of types of data by discharging ink through nozzles that are built into a recording head, e.g., an inkjet head, thus causing the ink to adhere to a sheet of printing paper or other recording material. Such an inkjet printer has many advantages, including making little noise, being capable of high-speed printing, and being usable with a wide range of recording material. Among the inkjet heads, a type of inkjet head that applies thermal energy to the ink when discharging the ink through the nozzle has such advantages as being very responsive to a print signal and lending itself easily to high-density integration (see U.S. Pat. No. 4,723,129 and U.S. Pat. No. 4,740,796).
The inkjet printer that uses such an inkjet head, on the other hand, is prone to experiencing a discharge malfunction with some or all of the inkjet heads, whether due to the nozzle being clogged by a foreign substance, an air bubble interfering with an ink supply path, or a change in a wetness level (wettability) of a nozzle surface, among other causes. Particularly where high-speed printing is concerned, when using a full-line type of inkjet head, upon which is mounted a plurality of nozzles, corresponding to a full width of the recording material, an important issue that has emerged is that of identifying the nozzle among the plurality of nozzles where the discharge malfunction has occurred, providing for compensation of a portion of an image corresponding to the malfunctioning nozzle, and taking the compensation into account in a recovery process of the inkjet head. The inkjet printer that employs such an inkjet head also suffers from a situation wherein a quantity of ink that is discharged from each respective nozzle may change in conjunction with a temperature change in the inkjet head, and a density of the printed image will not be reliable. It is particularly crucial where the full-line type of inkjet head is concerned to curb a degradation of the image that might result from such a change in the quantity of ink discharged.
In view of the foregoing crucial factors, a variety of types of methods for detecting when the ink is not being discharged, compensating for failure to discharge, control methods and apparatuses, and a variety of methods for controlling the quantity of ink discharged have long been promulgated.
Japanese Examined Patent Publication No. H04-006549 discloses a method that detects, in an ink discharge source, whether or not the ink is being discharged. According to the document, a conductor, the resistance thereof changes in response to heat, is placed in a position from which it can detect the heat that is emitted by an electrothermal transducer, i.e., a heater, and an application of the discharge signal to the electrothermal transducer controlled in response to a change in temperature as signified by a degree of change in a value of the resistance of the conductor.
Another method that detects, in an ink discharge source, whether or not the ink is being discharged is disclosed in Japanese Patent No. 2,831,778, wherein is disclosed an inkjet heard wherein the electrothermal transducer (heater) and a temperature sensor are both mounted on a silicon wafer or other support, and a temperature sensor that is configured of a film is overlaid with an array region of the electrothermal transducer. Japanese Patent No. 2,831,778 further discloses that the array region of the heaters is completely contained within an array region of the temperature sensor, which in turn is positioned as an overlay of the array of the heaters, thus improving the precision and the responsiveness of the detection and the control of the temperature.
Japanese Patent Laid Open No. 2002-178492 discloses a technique of detecting a temperature attribute of the inkjet head by determining a threshold value of detecting a remaining quantity of the ink in accordance with the temperature change that occurs when a specified energy is applied to a heater of the inkjet head.
As a proposal concerning each respective type of discharge malfunction determination criterion or condition for the purpose of improving the precision of the temperature detection, it has been suggested that the inkjet head be protected from an excessive increase in heat, for example, and performing a high-precision detection of a discharge malfunction. According to the proposal, Japanese Patent Laid Open No. H07-052408, a ranking of the inkjet head is performed according to a value of a resistance of a dummy resistor, and the determination condition of whether or not a discharge malfunction has occurred is changed according to the ranking.
As an inspection method that detects an ink discharge status of the inkjet head, there is an inspection method disclosed in Japanese Patent Laid Open No. H11-138788, wherein a temperature increase and a temperature decrease are measured commensurate with a level of heat increase that does not allow the ink discharge, and the temperature increase and the temperature decrease of the inkjet head are measured on a timing different from a timing of a print operation, pertaining to a preparatory ink discharge. If the ink discharge malfunctions, the temperature increase and the temperature decrease of the inkjet head are measured, a heat attribute of the inkjet head is provisionally obtained according to a print status monitoring step, and a determination is made as to whether or not the ink is being properly discharged from the inkjet head, in accordance with a result of a comparison of the measurements.
Neither Japanese Examined Patent Publication No. H04-006549 nor Japanese Patent No. 2,831,778 disclose specifying the position of each respective nozzle of a discharge malfunction. Nor is each respective detection circuit that detects the degree of change in the value of the resistance according to the heat that is emitted by the electrothermal transducer made clear. Consequently, it is not possible to identify the nozzle that is experiencing the discharge malfunction.
The conventional examples of Japanese Patent Laid Open Nos. 2002-178492, H07-052408 and H11-138788 do not disclose a technique of detection pertaining to multiple nozzles, given that they focus on detecting the discharge malfunction on a per inkjet head basis. Accordingly, there is no mention of identifying the malfunctioning nozzle of the inkjet head. Given that the threshold is computed solely from a detected thermal attribute, no consideration has been given to a precision in detection that corresponds to an electrical attribute or a plurality of different thermal attributes. The inkjet printer in Japanese Patent Laid Open No. H07-052408 employs a ranking based on the heater attribute of the dummy resistance. The ranking substitutes a select thermal attribute with the electrical attribute, however, and thus, does not have the improvement of improving the precision in detection based on the detected value of the thermal attribute as its objective.
Therefore, it would be desirable to solve the foregoing problems indigenous to the conventional technology.